So this was the "new" menu card on the transcon flight. Its basically the same, but on the "dinner" part you can see that they serve dinner only from flights departing between 4PM and 9PM. And many eastbound transcon flights depart after 9PM, and arrive early in the morning. As far as I know DL don't have any westbound flight departing after 9PM, so this restriction applies only for those who travel a redeye from the west coast.
Since my flight was half empty, I talked a lot with the FA at the galley, and also I asked the about this change. He told me the standard marketing ........ they were told to say, which is the following: in these overnight transcontinental flights people only want to sleep, as soon as possible, and also his personal experience is that, only about 20% of passengers took the meal, because really everyone wants to sleep, so they now just do a quick beverage and snack service (giving everyone 2 snacks, and if you ask 2 different snacks, you get 4 (2 of each)), on the 757 with two carts, so it really was quick.
I seated at an exit row window seat in economy, with no one next to me, so I refused the Comfort+ middle seat upgrade, but the FA confirmed they neither have any meal for C+. The only difference is still the one free beer, and that few more inches. Delta one of course still have gourmet dining (interenting... they don't want to sleep as soon as possible???)
He told me they started this updated policy from early October 2018.